Most people overestimate the quality of their diet, study shows

New research has found that most people in the United States substantially overrate the quality of their diet.

The study, presented this week at Nutrition 2022 Live Online,  the annual meeting of the American Society for Nutrition, was led by Jessica Thomson, PhD, research epidemiologist with the U.S. Department of Agriculture’s Agricultural Research Service. The investigators assessed whether the question, “How healthy is your diet?” could be used as a screening tool for nutrition studies — to replace or complement the dietary questionnaires commonly used in nutrition research.

“We found that only a small percentage of U.S. adults can accurately assess the healthfulness of their diet, and interestingly, it’s mostly those who perceive their diet as poor,” Thomson said in a statement.

The study used data from the National Health and Nutrition Examination Survey, a nationally representative survey of U.S. adults conducted every two years. Participants were asked to complete detailed 24-hour dietary recall questionnaires and rate their diet as excellent, very good, good, fair, or poor.

The results from the questionnaires were used to score each participant’s diet quality. Examples of foods ranked as healthier included fruits and vegetables, whole grains, healthy fats, lower-fat dairy products, seafood, and plant proteins. Foods considered less healthy included refined grains and foods high in sodium, added sugars or saturated fats, according to the organization.

The study revealed significant disconnects between the researcher-calculated scores and how participants ranked their own diet. Out of over 9,700 participants, about 8,000 (approximately 85 percent) inaccurately assessed their diet quality. Of those, 99 percent overrated the healthfulness of their diet.

Accuracy was highest among those who rated their diet as poor, among whom the researcher’s score matched the participant’s rating 97 percent of the time, according to the findings. The proportion of participants who accurately assessed their diet quality ranged from one percent to 18 percent in the other four categories.

“It’s difficult for us to say whether U.S. adults lack an accurate understanding of the components of a healthful versus unhealthful diet or whether adults perceive the healthfulness of their diet as they wish it to be—that is, higher in quality than it actually is,” said Thomson. “Until we have a better understanding of what individuals consider when assessing the healthfulness of their diet, it will be difficult to determine what knowledge and skills are necessary to improve self-assessment or perception of one’s diet quality.”